FIG. 2 shows a schematic structure of a system for interconnecting to communication networks 30 and 40. The interconnection is handled by a connectivity layer 10 and a control layer 20. The connectivity layer 10 has so-called media gateways (MG) 11 and 13 that handle the transport of call content or payload for calls between the communication networks 30 and 40. The media gateways 11 and 13 in the connectivity layer 10 handle data on the basis of an appropriate transport scheme, which can be STM based (Synchronous Transfer Mode), ATM based (Asynchronous Transfer Mode) or IP based (Internet Protocol), to name a few examples. The control layer 20 provides call related functions such as actual call control functions (e.g. session management, billing, etc.), as well as network service functions (e.g. intelligent network services) and other network application functions.
Traditionally, communications in telephone networks are circuit switched. Circuit switching is a technique in which a call connection between two terminating equipments corresponds to the allocation of a prescribed set of physical facilities that provide a transmission path of a certain bandwidth or transmission capacity. These facilities are dedicated to the users (terminating equipments) for the duration of the call. The concept of circuit switching is well known in the art and needs not be described in further detail.
Traditional mobile communication systems (such as GSM) also employ circuit switching. However, in recent years developments have been undertaken to introduce so-called packet switching for communication networks, especially for mobile communication networks. Packet switching means that the communication system transports information among users by transmitting sequences of packets each comprising part of the information. If the information does not fit into a single packet, the sending terminal equipment partitions the information into a sequence of packets, the sequence is transported across the network and the receiving terminal equipment reassembles the packets into messages.
The advantage of packet switching over circuit switching is that physical facilities do not need to be dedicated for the users of a given communication for the duration of that communication, such that a more efficient use of the network is enabled. Namely, in circuit switching the physical facilities (e.g. a predetermined amount of bandwidth on a trunk) are reserved for the specific circuit switched connection, even if the users of the associated communication are not exchanging information. In packet switched communication, transmission facilities are only used on demand, i.e. if there is information to be transported. As bandwidth is a very important resource in mobile communication systems, the more efficient use of bandwidth by using packet switching is of great importance.
Consequently, the future mobile communication systems will employ packet switching. An example of this is the General Packet Radio Service (GPRS).
A problem with the new development of mobile communication systems is the compatibility with circuit switched techniques. Namely, it is desirable that a given mobile communication system supports both circuit switched communications and packet switched communications. This effectively means that a mobile communication system comprises a plurality of so-called access networks, where some of these access networks are based on packet switching and others on circuit switching. This, however, leads to a complicated structure of the call control layer, because calls to and from mobile stations operating in the various access networks must be appropriately handled.
Object of the Present Invention
The object of the present invention is to provide an efficient call control network for controlling calls in a mobile communication network, where said mobile communication network comprises at least one circuit switching access network and at least one packet switching access network.